1. Field of the Invention
The present invention relates to a cutting tool machining method, and a wire electric discharge machine.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2013-111691 discloses a wire electric discharge machining method for machining, with high precision, a rotating-type cutting tool to which a polycrystalline diamond (PCD) material or a polycrystalline cubic boron nitride (PCBN) material is attached as a cutting blade. The PCD material and the PCBN material are cutting-tool materials having the highest degree of hardness.
As shown in FIGS. 28A and 28B, in this wire electric discharge machining method, a rake face that becomes a PCD-material blade that is brazed to a PCD tool is measured in advance by a touch sensor fixed to an upper guide portion of a wire electric discharge machine. A machining program is created based on the measured measurement data, and wire electric machining is performed based on the machining program.
In the wire electric discharge machining method disclosed in Japanese Patent Application Laid-Open No. 2013-111691, when rotational run-out occurs during rotation positioning of the PCD tool attached to a rotary axis, a problem arises in that a run-out error occurs in the outer circumferential dimension of the machined cutting blade section. As shown in FIGS. 29A, 29B, and 29C, when cutting is performed by a rotation tool that has a rotational run-out error, machining defects, such as a dimensional error in product machining and machining vibrations caused by the run-out, occur. Product precision is thus adversely affected.
As shown in FIG. 30, conventionally, a rotation tool is attached to a three-jaw chuck or a four-jaw chuck that is attached to a rotary axis. The chuck position is adjusted so that rotational run-out accuracy is maintained within acceptable limits when the rotation tool is rotated around the rotary axis. In addition, as shown in FIG. 31, when the rotation tool is fixed to a detachable collet-type holder capable of reproducing the position for attachment and removal to and from a face plate of the rotary axis, the position of a fixing jig for attachment and removal that attaches the collet holder to the rotary axis is required to be adjusted in advance so that the collet holder is accurately attached at the center of rotation.
In a high-precision rotation tool, the acceptable value for rotational run-out accuracy of the rotation tool is ordinarily 0.010 mm or less. Taking into account machining errors that occur during production of the rotation tool, the rotational run-out that occurs during rotation by the rotary axis is required to be kept within the acceptable limits. Such position adjustment requires expert adjustment techniques and a large amount of man-hours. In particular, when the three-jaw chuck or the four-jaw chuck, which are less expensive than the detachable collet holder, is used, the rotational run-out adjustment operation is required to be performed every time a tool is exchanged, and a large amount of man-hours is required. When the collet holder is used, because only a tool having an outer diameter that is compatible with the inner diameter of the collet can be attached, a large number of expensive collets are required to be provided to support various tool outer diameters.
Even in the case of the detachable collet holder in which position adjustment at the center of rotation is performed in advance, it is difficult to fix the tool exactly at the center of the collet because of tolerances in the collet inner diameter and the tool outer diameter. However slight, misalignment from the center and tilting occurs, thereby causing positional misalignment during production of the rotation tool and leading to a rotational run-out error.
In addition, in a centering apparatus and a centering method disclosed in Japanese Patent Application Laid-Open No. 2012-143830, the outer circumference of a rotation body is measured at two points in a +X direction and a −Y direction, and a position α of a center point between the two points is then calculated. In addition, the same outer circumference is measured at two points in a +Y direction and a −Y direction, and a position β of a center point between the two points is then calculated. α and β indicate the positionally misaligned centers of the rotation body. A misalignment amount R is then me rely calculated by √(α2+β2). This method cannot be applied to a wire electric discharge machine in which a wire electrode is stretched in an up/down direction and only the Y-direction position coordinate of a contact point on the outermost circumference of a tool can be obtained.
In addition, in Japanese Patent Application Laid-Open No. 8-171407, the circumference of the rotational run-out is measured by a proximity sensor. The run-out error is fitted by a sine curve, and a machining point is corrected based on the sine curve fitting. In this method, because the center of the rotational run-out and the maximum run-out width are not derived by calculation, all positions on the circumference are required to be measured by the proximity sensor. Therefore, correct measurement and correction are not possible for a tool, such as a cutting tool, that has three or four cutting blades and an incomplete cylindrical outer circumference in which a relief portion is formed as a notch in the tool outer circumference in a section in which the blade face is present.